Si nanowires grown by Al-catalyzed plasma-enhanced chemical vapor deposition: synthesis conditions, electrical properties and application to lithium battery anodes

Silicon nanowires have been synhesized using Al as a catalyst. Silane (SiH4) diluted in H2 carrier gas was employed as Si precursor in a plasma enhanced chemical vapor deposition system operated at various temperatures (450 °C and 550 °C). Those growth temperatures, which are lower than the eutectic temperature in the Al–Si system (577 °C) suggests a vapor–solid–solid growth mechanism. Four point resistance measurements and back-gated current-voltage measurements indicated that silicon nanowires were heavily doped (p type), with a doping concentration of a few 1019 cm−3. We have measured hole mobility values of ~16 cm2 V−1 s−1 at 450 °C and ~30 cm2 V−1 s−1 at 550 °C. Transmission electron microscope analyses showed that the silicon nanowires were highly twinned even when they grow epitaxially on (111) Si substrates. We have also evaluated the use of those highly doped Si nanowires for lithium-ion battery anodes. We have observed a good cycling behavior during the first 65 charge–discharge cycles, followed by a slow capacity decay. After 150 cycles at a charge–discharge rate of 0.1 C, the electrode capacity was still 1400 mAh g−1. The ageing mechanism seems to be related to the delamination of the SiNWs from the stainless steel substrate on which they were grown.